There is a limited amount of information available on the biomechanics of speech production. proposed in this application are four studies related to speech production biomechanics, two involving normal speech production and two involving abnormal speech production. One study of normal speech production is concerned with the effects of age and sex on laryngeal valving. In this study, laryngeal valving, as determined through measures of laryngeal airway resistance, will be documented in healthy men and women ranging in age from 20 to 80 years. The data obtained from this study will provide insight into normal mechanism and provide a normal data base against which to compare data from individuals with voice disorders. Another study of normal speech production will examine the development of velopharyngeal function. This will be a longitudinal study of subjects of both sexes, beginning at week 1 of life and continuing until the subject reaches 3 years of age. This study will provide physiologic evidence for the age at which velopharyngeal closure occurs for speech production and document patterns of velopharyngeal function during the first 3 years of life. This information will be relevant to understanding normal mechanism as well as providing a norm against which clinical data can be compared. One of the studies related to abnormal speech production involves documentation of the nature of speech breathing in individuals with spinal cord injury and of the effects of abdominal trussing on the speech breathing and speech of such individuals. This study represents the first formal attempt to examine the effects of abdominal trussing in general, and the effects of different degrees of trussing in particular. The results of this study will have direct clinical implications for individuals with spinal cord injury as well as individuals with impairments of the breathing apparatus caused by other neural disorders. Another study of abnormal speech production involves examination of the speech breathing of individuals with Parkinson's disease. The proposed study will provide detailed information regarding the speech breathing and general respiratory function of such individuals. This study will elucidate the influence of Parkinson's disease on breathing function, including speech breathing function, and may suggest better methods for evaluation and management of such function in clients with Parkinson's disease or other hypokinetic disorders.